P-doping of Si nanoparticles: The effect of oxidation

The radial dependence of the formation energy of substitutional phosphorus in silicon nanoparticles covered by an amorphous oxide shell is analysed using local density functional theory calculations. It is found that P+ is more stable at the silicon core. This explains the experimental observation of segregation of phosphorus to the Si-rich regions in a material consisting of Si nanocrystals embedded in a SiO2 matrix [Perego et al., Nanotechnology 21, 025602 (2010)]. Formation energy of positively charged substitutional phosphorus in a 1.5?nm diameter Si nanoparticle covered by a similar to 2?nm-thick amorphous SiO2 shell, as a function of its distance to the centre.